The present invention relates generally to opto-electronic devices subject to differential thermal expansion. More specifically, the present invention provides a solution to the problem of differential thermal expansion of adjacent WDM components and of adjacent parallel optical links components. Differential thermal expansion is particularly troublesome where the expansion directly disturbs the optical pathway of the assembled opto-electronic device.
The present invention is particularly effective in preventing differential thermal expansion which otherwise would disturb the optical pathway in the multiplexer/demultiplexer design shown and described in U.S. application Ser. No. 09/347,490, which is incorporated by reference herein as though set forth in full. The problem of differential thermal expansion becomes quite significant as WDM devices and other opto-electronic devices are downsized. The miniaturized WDM device utilizes a zigzag optical pathway requiring precise relative location of lenses, filters, lasers and photodetectors. Any differential thermal expansion which disturbs the relative location of those critical elements in the optical pathway has a severe effect on the performance of the assembled device. A contributing factor is that major components of miniaturized WDM devices have increased performance potential if materials can be used having different thermal coefficients of expansion. For example, major optical components are preferably made of molded plastic, which is not an efficient thermal conductor or heat sink. Materials such as ceramic, which are relatively efficient thermal conductors and heat sinks, have significantly different and smaller coefficients of thermal expansion as compared to molded plastic.
According to one embodiment of the present invention, a ceramic substrate is utilized in a miniaturized WDM device to support heat generating components such as lasers, laser driver chips and photodetectors. The ceramic substrate in the preferred embodiment is adhesively bonded to a metallic housing for the WDM device. Heat is efficient transferred from the heat source to the ceramic substrate and thence preferably to a metallic housing and into the ambient air. In order to reduce or prevent differential thermal expansion between the ceramic substrate and the molded plastic component to which it is connected, a plurality of sturdy molded stakes protrude from the plastic component and extend through and are adhesively bonded to holes in the ceramic substrate. As the assembled device heats up during operation, the plastic (having a much higher thermal coefficient to expansion than the ceramic) tends to expand faster than the ceramic substrate. However, that differential expansion is reduced or prevented by the stakes. Internal compressive stresses are generated within the plastic component, but those compressive stresses are tolerated by the plastic and the optical pathway is not disturbed.
A second embodiment of the invention applies to parallel optical links such as an optic coupler wherein a laser/detector array is mounted on a substrate or board and wherein the optic coupler is staked to the substrate or board supporting the laser or detector array.
A primary object of the invention is to reduce or prevent differential thermal expansion which would otherwise adversely affect the optical pathway of an opto-electronic device, such as a WDM device or an optic coupler.
A further object of the invention is to utilize a substrate to carry one or more heat generating components of an opto-electronic device, and to connect the substrate to an optical assembly in a manner which reduces or prevents differential thermal expansion between the substrate and optical assembly.
Another object of the invention is to provide a molded plastic optical assembly having a plurality of molded plastic stakes extending through and adhesively bonded to a substrate to reduce or prevent differential thermal expansion.
A further object is to provide a miniaturized WDM device having molded plastic components carried in a metallic housing wherein heat is efficiently transferred from a heat generating source carried on a substrate to said metallic housing, and said substrate is connected to said molded plastic component in a manner to reduce or prevent differential thermal expansion.